The present invention relates to a valve characteristic controller for use for an engine, and, more particularly, to a valve characteristic controller which can be suitably used for a direct injection type engine which directly injects fuel into combustion chambers.
Conventionally, a cam which has a sub lift portion on its cam face in addition to a main lift portion is known as an intake valve or exhaust valve to be used in a valve drive mechanism of an engine. The height of the sub lift portion changes in the axial direction of the cam. By moving a camshaft in accordance with the operational state of the engine, the position of the cam face that drives the valve changes in the axial direction. As a result, a valve lift pattern is changed to adjust, for example, the amount of an exhaust gas or the like to be taken into a combustion chamber of the engine. The exhaust gas to be taken into a combustion chamber significantly affects the combustion state or the like of the engine.
However, merely changing the height of the sub lift portion in the axial direction of the cam cannot realize a valve characteristic that sufficiently satisfies various engine performances demanded according to the operational states of the engine. Particularly, a direct injection type engine which directly injects fuel into combustion chambers needs complicated engine control as compared with an ordinary engine which feeds fuel and air, previously mixed, into combustion chambers, and a variety of engine performances are demanded. Therefore, it was not conventionally possible to realize a valve characteristic that could sufficiently satisfy the performances demanded of the direct injection type engine.
It is therefore an object of the present invention to provide a valve characteristic controller capable of realizing a valve characteristic that sufficiently satisfies various engine performances demanded.
To achieve the object, the present invention provides a valve characteristic controller for an engine that generates power by combusting a mixture of air and fuel in a combustion chamber. The engine has a valve for selectively opening and closing the combustion chamber. The valve characteristic controller has a cam for driving the valve, and the cam have a cam face about an axis thereof. The cam face has a main lift portion, which causes the valve to execute a basic lift operation, and a sub lift portion, which assists the action of the main lift portion. The main lift portion and the sub lift portion continuously change in an axial direction of the cam. The cam face realizes different valve motion characteristics in accordance with the axial position of the cam face. An axial movement mechanism moves the cam in the axial direction in order to adjust the axial position of the cam face that drives the valve.
As the cam is moved in the axial direction, the valve is provided with various valve lift characteristics which are a combination of a cam lift pattern realized by the main lift portion and a cam lift pattern realized by the sub lift portion. The main lift portion and sub lift portion which change in the axial direction cooperate with each other to ensure diverse adjustments of the valve characteristic. It is therefore possible to allow the valve characteristic to sufficiently match with various engine performances demanded in accordance with the operational states of the engine.